This study contains six weeks of active treatment with D-serine, riluzole or placebo. The decision to implement a 6-week treatment protocol was based on the following: a) the ability to gradual increase doses of medication on a weekly basis over the first five weeks to dosages beneficial in other conditions; b) a treatment duration similar to that used in other glutamate modulatory treatment studies; and c) a time period necessary to identify a treatment effect in milder non-neuroleptic tic-suppressing medications such as clonidine. We emphasize that this is a short term, proof of concept study for riluzole and D-serine in the treatment of tics. Specific questions such as long term durability of beneficial effects, potential long-term side-effects, and comparisons to non-drug interventions are important, but not a focus of this pilot study.